High-frequency electron discharge apparatus



Oct. 18, 1949. E, D MQARTHUR 2,485,400

HIGH'FREQUENCY ELECTRON DISCHARGE APPARATUS Filed April 19, 1945 Fig.1.

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Inverfitor: 7 Elmer D. Mc Arthur,

His Attorney.

Patented Oct. 18, 1949 ZAtSAW HIGH-FREQUENCY ELECTRON DISCHARGEAPPARATUS Elmer D. McArthur, Schenectady, N. Y., assignor to GeneralElectric Company, a corporation of New York Application April 19, 1945,Serial No. 589,231

2 Claims. (Cl. 31539) The present invention is directed to electronictubes and is primarily concerned with the provision of a new andimproved space charge control electron tube which employs the principleof sorting electrons in accordance with their velocities for increasingthe trans-conductance of the tube.

It is an object of my invention to provide a new and improved electronictube which is suitable for amplification of both low and very highfrequency signals. I

It is another object of my invention to provide a new and improvedelectron discharge device in which the anode current therein ismodulated by sorting of electrons in accordance with their velocity.

It is a still further object of my invention to provide new and improvedultra high frequency circuits employing cavity resonators.

One of the features of the invention is the employment in an electronictube of a pair of control grids spaced between an anode and a cathode,utilizing a first of these control grids to vary the velocity of theelectronic stream between the anode and cathode, and utilizing the otherof the control grids to sort out electrons in the stream in accordancewith their velocity.

The features of the invention desired to be protected herein are pointedout with particularity in the appended claims. The invention itself,together with further objects and advantages thereof, may best beunderstood by referring now to the following description taken inconnection with the accompanying drawing in which Fig. 1diagrammatically illustrates an electron discharge device and amplifyingcircuits suitably embodying my invention; Fig. 2 diagrammaticallyillustrates a modification of the electron discharge device of Fig. 1;and Figs. 3 and 4 are graphs illustrating certain operationalcharacteristics of the device of Fig. 2.

Referring particularly to Fig. 1, there is shown an electron dischargedevice having an anode I and a cathode 2 arranged in end-to-end order.The anode and cathode are in the form of cylindrical memberssubstantially coaxially aligned and having closed adjacent ends inopposed spaced relation to form electron emitting and electron receivingsurfaces. Disposed between the anode and cathode are a pair of controlgrids 3, 4, and a focussing grid 5. The envelope within which theseelectrodes are enclosed comprises a series of three circular metal parts6, 'l, and 8 which are supported in spaced relation by glass cylinders 9and I sealed between them. The

part 1 provides a terminal for the grid 4 and a terminal for the anodeis provided by a cylindrical enlargement H which is welded or solderedagainst the upper surface of the part 6. The grid 3 is supported fromthe metallic tube l2 which concentrically surrounds the cathode 2 andWhich is Welded or soldered to the part 8. The focussing grid 5 issupported by a metallic tube l3 disposed between tube 12 and cathode 2.The lower end of tube I3 is provided with flange I4 which parallels theunder surface of part 8, but which is separated therefrom by aninsulating washer I5. Similarly, the cathode 2 extends through a centralaperture in the part 8 and is provided, at its lower extremity, with aflange [6 which parallels the under surface of the part 8 but which isseparated from that part by an insulating spacer l! which may be, forexample, a mica washer. Preferably, the thickness of the insulatingwashers I5, I! is such that the cathode 2 has a high frequencyconnection with the part 8 through the capacity existing between thispart and the flange IE, but is effectively insulated from the part 8 andthe part M as far as direct currents and low frequency alternatingcurrents are concerned. Separate connections are made to the cathode andgrid 5, respectively, for direct currents and low frequency alternatingcurrents by means of lead-in wires l8, l9 secured to the under surfaceof the part I2 and tercurrent to a coiled filament 24 arranged withinthe cathode cylinder 2. I

For the amplification of high frequency voltages, the electronic tube isincorporated into a cavity resonator forming structure which comprisesan outer elongated conductive cylinder 25 having an inwardly flangedportion 26 which surrounds the base portion of the part 8, beinginsulated therefrom by a cylindrical insulator 21,

I a centrally disposed, conductive member 28 which abuts against theouter surface of disk 6 and is conductively connected to the anodeterminal I I,

and an intermediate conductive cylinder 29 which is conductivelyconnected to the grid disk I through a spring contact arrangement 30. Inthis cavity resonator, the outer cylinder 25 is insulated from the part8 by the insulator 21, but is connected to this part for high frequencyalternating currents through the capacity existing between the flange 26and the part 8. The

' anode cylinder 28 is supplied with unidirectional currents over alead-in conductor or rod 3|. An extension 32 of the anode cylinder 23concentrically surrounds the rod 3|, being insulated therefrom at oneend by an insulating washer 33 disposed between the adjacent ends ofparts 28 and 32 and at its opposite end by a washer 34 which, inconjunction with a nut 35, serves as means for clamping the parts 28 and32 and maintaining them in axial alignment. The structure thus describedforms a pair of cavity resonators, one defined by the cylinders 25 and29 and coupled to the space between the grids 3, 4" and the otherdefined by the cylinders 28, 32 and intermediate cylinder 29 and coupledto the. space between anode and grid 4. The dimensions: of these cavity.resonators may be adjusted by means of sliding plungers 36, 3'! and rods38, 39 connected to these plungers.

The D. C. connections for the discharge device may be made in variousways and, in the arrangement illustrated, the anode is maintained at apotential above ground being. supplied with that potential by a lead-inconductor 4|! connected to the rod 3|, while the cathode is maintainedat essentially ground potential. The focussing grid is maintainedslightly negative with respect to the cathode 2 by means of a lead-inconductor 4| connected to prongs 2|. For purposes to be explained later,the second control grid 4 is maintained: at or near ground potential,while the first control grid 3 is maintained at a. positive potential.with respect to the cathode, being connected by means of lead 42 to asuitable source of voltage, such as the battery 43.

Signals to be amplified are supplied to the cavity resonator formed bthe cylinders 25, 29 over a concentric transmission line comprising atubular outer conductor 44 and a centrally disposed inner conductor 45terminating in acapacitive coupling plate 46 disposed within this cavityresonator in spaced relation with the outer surface of intermediatecylinder 29. Amplified signals may be extracted from the cavityresonator coupled with the anode-grid 4 space, for utilization in anexternal circuit by means of a coupling loop 41 which extends into. thisanode-grid cavity and which is supported from a hollow tubular conductor48 extending outwardly through the plunger 31. A Wire 49, which connectswith one extremity of the coupling. loop 41 is arranged within theconductor 48 and forms with it a coaxial transmission line.

In the operation of the system of Fig. 1, for the amplification ofsignals supplied. over input transmission line 44, 45', the dimensionsof the cavity resonator defined by the members25, 29 are; adjusted bypositioning of the plunger 36 to resonate at the frequencies of the,input signals. The grids 3, 5 preferably are aligned, and the grid 5 issupplied with a focussing potential so that electrons from th cathode 2do not strike the. wires of the grid 3. The grid 3 is maintained at apositive potential to accelerat electrons emittedby the cathod 2. Asthe'focussed electrons from the, cathode 2 traverse the region betweenthe wires 3 and 4,. they are either further accelerated or deceleratedby the electromagnetic fields existing between. these wires. The grid 4is maintained at a potential which is substantially that of the cathode2 or slightly negative with respect to the potential of thi cathod inorder to refiect those electrons which are decelerated' in traversingthe region between the grids 3', 4. As a result,,on1 e1ectrons which areaccelerated in this region pass, through the grid .4 4 to excite theoutput cavity defined by the members 28, 29 and supply energy to theoutput coupling loop 41.

In the modification of my ultra high frequency system shown in Fig. 2,the electron discharge device th-ere employed differs from that of thedevice of Fig. 1 in that it is so constructed that inputs signals may beimpressed between the cathode 5D and a first grid or control electrodeThe electron discharge device of this system includes, in addition tothe mentioned electrodes, an anode 52 and two additional grids orcontrol electrodes 53, 55 supported between the electrodes 5| and theanode 52. The grids 53, 54 are provided, respectively, with supportingdisks 55, 56, while the grid. 5! is supported with a cup-shaped metallicdisk. 51. The disk 57 may be soldered or Welded to a metallic sleeve 58which concentrically surrounds the cathode 58, being spaced therefrom bya disk insulator 59. The sleeve 58 has an outwardly directed flange 60,and insulating. cylinders GI, 62, sealed respectively between themembers 65, 55 and 55, 56, support the grids 5|, 53, 54. in spacedrelation. An additional insulating cylinder 63. is sealed between thedisk 56. and an enlarged flange portion 64 of the anode 52 to completethe enclosing envelope of the. discharge device. The cathode 50 isheatedby a filament 65 whichis enclosed within the cylinder which forms thecathode.

The input circuit of the system of Fig. 2 comprises a cavity resonatorof the concentric conductor type constituted by an inner conductor 66which slides over the cathode cylinder 59 and a tubular outer conductor61 which slides over the metallic sleeve 58. and the cathode cylinder 56form a portion of this cavit resonator. The dimensions of the resonatormay be adjusted by means of a plunger 68 and input signals may besupplied over a concentric transmission line comprising a tubular outerconductor 69 and a centrally disposed inner conductor 18 terminatinginan input. electrode or probe H of the capacitive type. The outputcircuit of the system likewise is in the form of a cavity resonator ofthe concentric conductor type and' comprises an inner conductor 12 andcapacitively coupled through an insulator 13 with a cylindricalenlargement 14 attached to the outer surface of the anode. The outerconductor of the output resonator is in the form of a metallic cylinder15 having resilient fingers 16 engaging the disk 56. The dimensions ofthis output cavity resonator may likewise be adjusted by means ofplunger H to adjust the resonance frequency of the resonator. Energy maybe extracted from the resonator by means of an output coupling loop 18.

Unidirectional potentials for operating the device 2 are supplied to theanode 52 over a conductor 19. The cathode 5|] is preferably maintainedat ground potential and a negative potential is supplied to the grid 5|over a conductor connected with the sleeve 53, the sleeve 58 and theouter conductor 61 of the input resonator being insulated by acylindrical insulator 8! to permit the impression of unidirectionalpotentials between the cathode 59 and the electrode 5|. The controlelectrode 53 is provided with positive potential by means of a conductor82 connected to the disk 55. The reflecting electrode 54 preferably isoperated at the potential of the cathode or slightly negative withrespect thereto, such potentials being supplied directly to thesupportingdisk 56 for this electrode.

In this way, the sleeve 58v In the operation of the system foramplification of signals supplied to the input circuit over thetransmission line 69, 10, the grid 53 is maintained at a positivepotential to accelerate electrons emitted from the cathode 50 and thegrid 54 is maintained substantially at the potential of the cathode orslightly negative with respect to the potential of this cathode in orderto repel or reflect the emitted electrons. Thus, between the grids 53,54, there are present electrons flowing in both directions. Both thequantity of electrons and the transit angle inthe region between thesecontrol electrodes may be controlled by the magnitude of the positivepotential applied to the grid 53 so that the system does not oscillate.

The condition which exists when a signal to be amplified, is supplied tothe input resonator may best be explained by reference to the curves ofFigs. 3 and 4. The current flow, i in the plane of the grid 53 is shownby the curve 83 of Fig. 3. This current of course varies in magnitudewith the potential impressed between the cathode and grid 5| that is, inaccordance with the variations in the electromagnetic field in the inputresonator. The average value of the current, Iav, is indicated by theline 84 of Fig. 3. The velocity of the electrons, which varies with theaccelerating fields existing between the cathode and the grid 5|, isshown by the curve 85 and the average velocity of the electrons in theplane of grid 53 is shown by the straight line 86. If the voltage ongrid 54 is made such that electrons having a velocity Dav cannot passgrid 54, then those electrons arriving at the grid 54 between the timest1 and t2 pass through the plane of grid 54 to the anode, while thosewhich arrive at the plane of grid 54 between the time t: and the timeits are reflected and returned partly to the grid 53 and partly to thecathode 50.

Those electrons which pass through the grid 54 give a current flow atthe anode which is shown by the curves of Fig. 4. The overall effect atthe anode of the accelerating potential applied to the grid 53 and thereflecting potential applied to grid 54 is to provide a large flow ofcurrent during positive halves of each cycle and zero flow of currentduring negative half cycles so that, for all purposes, a very largetrans-conductance of the electronic tube is obtained.

Since the time of transit of electrons between the planes of the variouselectrodes is an appreciable part of and frequently more than a cycle,the voltages impressed may be so related with respect to the frequenciesof the signals to be amplified that electrons reflected at grid 54reenter the spacing between grid 5| and the cathode on a subsequentretarding half cycle of the excitation voltage. With this relationbetween transit time and potentials, the presence of these returningelectrons in the cathode-grid 5| space increases the space charge with aresultant decrease in the velocity of forward moving electrons, thusessentially increasing the modulating effect of the excitation signalson the electron stream of the device. The effect, therefore, ofintroducing signals into the input cavity is to modulate the electronstream passing between the cathode 5|! and the control electrode 54,that is, electrons of this stream are sorted in accordance with theirvelocities. On positive half cycles, current pulses penetrate the grid54 and flow to the positively charged anode. The modulated current whichflows between the grid 54 and the anode excites the output cavitydefined by the cylinders I5, and

12, 13 and is suppliedto utilization circuits by means of the outputcoupling loop 18.

The foregoing considerations apply of course only when the electrondischarge device is operated as a space charge limited electronic tube.The modulation of electron velocity takes place in the interaction spacebetween the cathode 50 and the control electrode 5|, while thereflection of electrons having a velocity less than the value Dav iseffective between the grid 53 and the grid 54. As a result of theseeifects, there are many more than the normal number electrons or chargesbetween the cathode 50 and the grid 54. This increase is due to the factthat electrons are both traveling from the grid 54 to the cathode andreturning to the cathode from the grid 54. It is apparent of course thatthe number of electrons between the cathode and the control grid 53establishes the magnitude of the current whic flows to the anode- In theforegoing, the system of Fig. 2 has been described as an amplifler.- Itis apparent, of course, that the systems of both Figs. 1 and 2 may beemployed as a source of oscillations. This is indicated in Fig. 2 by thedotted feedback connection, as shown by a coupling probe 81 and theinput probe 1 the feedback being made over a concentric transmissionline connecting these two probes. In the operation of the structure asan oscillator, the grid 5|, being maintained at a negative potential,operates to focus the electron beam emitted by the cathode 50. One ofthe advantages of the structure is that concentration of the electronsin the interelectrode space into a beam through the action of thenegative focussing electrode 5| results in a reduction of current at thepositively charged electrode 53. The overall efiect is to increase thespace charge density and to provide higher power output for theoscillator.

It is apparent also that the principles which are employed in thesystems of Figs. 1 and 2 for the amplification of high frequency signalsare applicable also to the generation or amplification of low frequencysignals, the result being obtained by sorting of electrons in accordancewith their velocities to permit only those having a velocity greaterthan a threshold level to travel to the anode of the device.

While I have shown and described my invention as applied to particularsystems embodying various devices diagrammatically shown, it will beobvious to those skilled in the art that changes and modifications maybe made without departing from my invention and I aim in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An ultra high frequency circuit comprising an electron dischargedevice having an anode cylinder and a cathode cylinder coaxially alignedtherewith, said cylinders having adjacent closed ends in opposed spacedrelation, three control grids positioned between said ends, threetransverse conductive members connected respectively to said anode andtwo of said control grids, a pair of cylindrical insulating memberssurrounding said anode and cathode cylinders and sealed respectivelybetween said transverse conductive members, a conductive cylindersurrounding said cathode supporting the third of said grids, meansconnected to said third grid for maintaining said grid at a negativepotential with respect to said cathode fito ifoc'us electrons remittedtherefrom, means connectdfltothe said two of. said "control gi idsforasupplysing afi high 'frequency :signal r-to" be amplifiectb'etweensaid twoz'grids;meansconnecteclztd theione' ef saidtwo grids a'djacentsaid cathodei f ormaiintaining said-'grid at a positive'potential WV-1thi 'respect' -to salicl cathode to accelerate electrons emittedtherefromgmeans connected to thenether df-=Said1two grids for:maintaining said grid. substantially #atLthe potential of said cathodeto sso'rt electrons r-passin'g between =said cathode andaanode: inaccondance withtheir velocities.

i2. kAn electrcn dischargeudevice 'com'prising' an anode an'dua cathdd'ehaving planar surfaces in opposed spaced relation, apair-of:grids'interposed between said surtacesi tl-iree transverseconductive men i'bers'con d-uctivly supportingxsaid anode and saidgridsrinz spaced relation and a'fiording extemri'aily :=a'cces'sib1eterminals therefor, -means maintaining said transverse members in spacedreiatiomlapcyliinderrexteriding'inea direction transversettot sai'dcanductive membersconstituting a -REFERENGES .GIlT ED "The f o'llowing"references are 6f "record in the file ("if this patent:

UNITED STATES PATENTS Number Name Date ::2',2'Z2;374 Kallmannet al-J'Fb. 10, I942. "2,278,210 "Morton ='Mar. 31, 1942 "2,353,743 *McArtnurJuly 18, 1 944 2,395,043 Goodchild Feb. 1 9, 19.46 914002753 Haeff May'21, 1946 2,402, 6I2 Dod i ngton J-u1y' "25, 1946

